As for a method for cleaning a wafer for semiconductor devices after a dry etching process or the like, there is employed a wet type substrate cleaning method. This method removes foreign materials, e.g., particles, by dipping a wafer to be cleaned in solution or solvent or by spraying solvent or solution onto the wafer to be cleaned and then rinses the wafer to be cleaned with pure water if necessary.
In the wet type substrate cleaning method, the solvent or the solution may remain on a surface of the substrate after a cleaning process, which may cause watermark, surface oxidation or the like. In order to cope with such case, a spin dry process is provided to dry and remove the remaining solution, pure water or the like, after, e.g., a batch dipping process or a spraying cleaning process (see, e.g., Japanese Patent Application Publication No. 2008-41873).
In the spin dry process, when the solution, the pure water or the like is volatilized, liquid-vapor interfacial tension acts on a protruded pattern formed on a wafer surface and, thus, the pattern collapses. Further, when a wafer has a so-called low-k film, it is easy for the solution, the pure water or the like to be deposited in a porous portion of the low-k film. Once the liquid is deposited therein, it cannot be completely removed.
On the other hand, there is suggested, by the present inventors, a wafer dry cleaning method (see, e.g., Japanese Patent Application No. 2008-276027) using a cleaning apparatus including: a chamber; a mounting table provided in the chamber, for mounting and heating a wafer; and a collecting plate disposed to face the mounting table in the chamber. In this method, the chamber is depressurized and the wafer is heated to peel off particles from the wafer by thermal stress. Further, the peeled-off particles move to the collecting plate by thermophoretic force generated by a temperature gradient between the wafer and the collecting plate.
However, as the dry cleaning method is repeated, the number of particles attached to the collecting plate increases and this may lead to secondary contamination in which the particles fall from the collecting plate to be attached to the wafer. For that reason, the particles attached to the collecting plate need to be removed by cleaning the collecting plate regularly. When the collecting plate is taken out for cleaning from the cleaning apparatus, times and efforts are required. Moreover, the cleaning of the collecting plate in the chamber may cause the secondary contamination in which the particles removed from the collecting plate freely scatter in the chamber to be attached to other components in the chamber.